1. Field of the Invention
The present invention relates to a selective or spot electroplating apparatus, hereinafter referred to as a "selective plating apparatus", and, more particularly, to such an apparatus having a cleaning device for plating an elongated strip of metal, hereinafter referred to as "strip", in a predetermined interval in the lengthwise direction thereof.
The selective plating apparatus of this type can be advantageously employed for plating required portions of a lead frame that is used for the manufacture of semiconductor devices, for example integrated circuits, (IC's) and large scale integrated circuits (LSI's). In this case, the lead frame strip has a number of consecutive, identical segments formed in the lengthwise direction, wherein each segment is formed at the central portion thereof. Each segment includes a die-bonding area on which a semiconductor chip, such as an IC or LSI, is mounted and a number of leads having their tip ends, i.e., a wire-bonding area, surrounding the above-mentioned die-bonding area.
2. Description of the Prior Art
A selective plating apparatus adaptable for plating lead frames of this kind is known in the prior art, and comprises masking means having an aperture which allows electrolyte or electroplating liquid to be sprayed only onto the required portions of the lead frame, i.e., a die-bonding area and a wire-bonding area formed therearound at the central portion of each segment, and prevents the electrolyte from affecting the other portions. According to such a selective plating apparatus, the electrolyte discharged from a nozzle is sprayed onto the predetermined area of a substrate and, at the same time, an electric voltage is applied between an anode and the cathodically charged lead frame to form a desired electroplated metal layer.
When conducting selective plating with a masking means onto a lead frame, the strip is conventionally supported directly between a masking member and a back-up plate and the electrolyte is applied to the strip through an aperture of the masking member. Therefore, if the masking member and back-up plate used to support the strip therebetween are dirty or stained, the quality of the electroplated strip would be considerably reduced. Consequently, if excess electrolyte adheres to the masking member or the back-up plate, and also adheres to the strip per se, the plating metal may be electrolytically replaced or substituted and appearance and function of the plated product may be significantly damaged. Especially, when silver was used for electroplating, the electrolytical replacement would readily take place. Therefore, it has long been felt necessary to provide means for cleaning the strip, the masking member, and the back-up plate at each cycle of selective plating.